The present invention relates to a method of determining an initial pressure in a motor vehicle brake system and a pressure control device for implementing the method.
For the optimal application of electronic brake systems, in particular anti-lock systems (ABS) and driving stability control systems (e.g. ESP), it is favorable to drive—with inlet and outlet valves being respectively associated with a wheel brake cylinder—by taking into account the so-called initial pressure, i.e. the pressure between the master brake cylinder and the inlet valve. It is possible to sense this pressure using a pressure sensor, however, sensors which are appropriate for this purpose are very expensive.
Document DE 199 46 777 A1 discloses a method which, for assessing an initial pressure that prevails between a master brake cylinder and an inlet valve of a wheel brake cylinder of a motor vehicle brake system, uses the follow-up voltage of a clock-operated motor of a pump which is provided for the return delivery of brake fluid from an accumulator chamber arranged on the outlet side of the wheel brake cylinder into the master brake cylinder, as well as using the accumulator chamber pressure determined or measured in the accumulator chamber. The accuracy of the assessed pressure value is not indicated.
The object of the invention is to provide a method which allows determining the initial pressure in an exact, reliable and simple manner.